Influence of Temperature on Bacterial Development in Waters

Microbiological stability in water mains has become an increasing problem for waterworks where more and more surface water is used for distribution requirements. Even when surface water is treated, appropriately, it usually contains a higher amount of organic compounds than does groundwater, and during certain periods, can attain temperatures between 20 and 25°C. Furthermore, ozonization applied during treatment modifies structures of the dissolved organic materials.

Twenty bacterial strains capable of aftergrowth were isolated starting from ozonized surface water, from water of subterranean origin, and from a mixture of these two types of water. Six typical strains were used to determine the importance of the temperature factor on aftergrowth in five types of waters of different characteristics.

Three criteria for the evaluation of aftergrowth are: the growth rate factor (r₂), the growth yield (maximum number of germs/mL when growth stops), and the latency time (in hours). The results, in triplicate, obtained from growth curves then were submitted to an analysis of variance by two cross classifications.

It was established that aftergrowth is related to the classical Pseudomonas and Azobacter families, but also to the species of Bacillus, Corynebacter, Micrococcus, Vibrionaceae, and even Enterobacter. Furthermore, it has been proven that the temperature factor is most important in all aspects, as an increase in water temperature enhances all growth characteristics: shortening of the lag-phase; increase in growth-rate factor; and yield.

Under practical conditions, the significant growth delay is very important. With Pseudomonas putida, the lag-phase is on the order of three days at +7.5°C and 10 hours at +17°C.